I don’t think you’re entirely correct about the voices…although they may be tweaked slightly, but that’s normal procedure in most music recorded in a studio, with retakes and splicing done by the producers and sound engineers to make a flawless recording. They have been filmed in the studio in their actual present day 70 + year old bodies singing the new songs. The rest is completely down to technology, recreating them singing in present day voices but with replicated 50 years younger bodies. Obviously the money is a big motive, although I hardly think it’s the main consideration or they’d have done it before now. They must still be very rich already with all the royalties from not just their still popular music, but the Mama Mia movie and stage show franchises. I think the challenge of using this new technology was the deciding factor for their new album and forthcoming virtual performance.

@Marionville yes, I never thought they were down to their last Kroner, so to speak. I remain sceptical about the authenticity of the voices, though you're right all music now is processed with tech these days to some extent. No doubt they are refreshing their finances at this stage of life and their families must be very happy.